ProfilesFile.read/1: drop [:safe] flag, trust our own files

The persisted grid_data files contain atoms (:base_m, :top_m,
:thickness_m, :min_freq_ghz, :native_min_gradient, :ducts, etc.) that
live in modules which aren't eagerly loaded during application start.
warm_grid_cache_from_latest_profile runs in Application.start/2 before
those modules get pulled in by their first call sites, so [:safe] was
rejecting our own legitimate files at boot — every weather page hit
crashed with "invalid or unsafe external representation of a term".

The whole point of [:safe] is to refuse atoms from untrusted external
ETF input. ProfilesFile.write!/2 in this same module is the only writer
of these files, so the input is trusted by definition — drop the flag.
The test additions round-trip the production data shape including duct
fields as a regression guard.

lib/microwaveprop/propagation/profiles_file.ex

@@ -67,11 +67,21 @@ defmodule Microwaveprop.Propagation.ProfilesFile do
   `{:ok, %{{lat, lon} => profile}}` or `{:error, :enoent}` if the file
   doesn't exist. Used by `Microwaveprop.Weather` to warm `GridCache`
   on pod startup without touching the database.
+
+  Does *not* pass `[:safe]` to `binary_to_term/1`. The file was written
+  by `write!/2` in the same code base, so we trust it. The previous
+  `[:safe]` flag was rejecting our own files at app-startup warm time
+  because some atoms in the persisted profile (`:base_m`, `:top_m`,
+  `:thickness_m`, `:min_freq_ghz`, `:native_min_gradient`, etc.) live
+  in modules that aren't eagerly loaded during boot, so they weren't
+  in the runtime atom table when `warm_grid_cache_from_latest_profile`
+  ran. The fix is not "load more modules eagerly" — it's "trust files
+  we wrote ourselves."
   """
   @spec read(DateTime.t()) :: {:ok, %{{float(), float()} => map()}} | {:error, :enoent}
   def read(%DateTime{} = valid_time) do
     case File.read(path_for(valid_time)) do
-      {:ok, binary} -> {:ok, :erlang.binary_to_term(binary, [:safe])}
+      {:ok, binary} -> {:ok, :erlang.binary_to_term(binary)}
       {:error, _} -> {:error, :enoent}
     end
   end

test/microwaveprop/propagation/profiles_file_test.exs

@@ -56,6 +56,47 @@ defmodule Microwaveprop.Propagation.ProfilesFileTest do
     test "returns :enoent when no file exists" do
       assert ProfilesFile.read(~U[2026-04-14 18:00:00Z]) == {:error, :enoent}
     end
+
+    test "round-trips the full production data shape including duct fields" do
+      valid_time = ~U[2026-04-14 18:00:00Z]
+
+      grid_data = %{
+        {32.75, -97.125} => %{
+          surface_temp_c: 25.0,
+          surface_dewpoint_c: 15.0,
+          surface_pressure_mb: 1013.25,
+          hpbl_m: 750.0,
+          pwat_mm: 32.5,
+          run_time: ~U[2026-04-14 17:00:00Z],
+          precip_mm: 0.0,
+          wind_u: 3.2,
+          wind_v: -1.7,
+          cloud_cover_pct: 25.0,
+          native_min_gradient: -78.4,
+          best_duct_freq_ghz: 24.0,
+          duct_count: 1,
+          max_duct_thickness_m: 200.0,
+          ducts: [
+            %{base_m: 200.0, top_m: 400.0, thickness_m: 200.0, min_freq_ghz: 10.0}
+          ],
+          profile: [
+            %{"pres" => 1000.0, "tmpc" => 25.0, "dwpc" => 15.0, "hght" => 50.0}
+          ]
+        }
+      }
+
+      ProfilesFile.write!(valid_time, grid_data)
+
+      assert {:ok, round_tripped} = ProfilesFile.read(valid_time)
+
+      point = round_tripped[{32.75, -97.125}]
+      assert point[:surface_temp_c] == 25.0
+      assert point[:run_time] == ~U[2026-04-14 17:00:00Z]
+      assert [duct] = point[:ducts]
+      assert duct[:base_m] == 200.0
+      assert duct[:thickness_m] == 200.0
+      assert duct[:min_freq_ghz] == 10.0
+    end
   end
 
   describe "list_valid_times/0" do